Then came word late Friday afternoon that the vast majority of the ballots in the hand recount across the state are unlikely to help Nelson because voters chose to skip the Senate race altogether. That recount was considered a linchpin of Nelson's already uphill strategy to victory.

Most experts say Nelson now needs a miracle to erase Republican challenger Rick Scott's 12,603-vote lead, formalized after Thursday's machine recount ended. A hand recount of disputed ballots that were set aside because the machines had trouble counting them is now being conducted.

"He can pull this off but everything has to go his way," said Charles Zelden, a political science professor and election recount expert at Nova Southeastern University in Florida. "And any one small glitch can be enough to keep him from winning."

At this point, Nelson has until Sunday at noon to pull off his long-shot bid. Barring a court ruling, that's the deadline for canvassing boards at each of Florida's 67 counties to report their final recount tallies to the state.

Marc Elias, Nelson's lead recount attorney, admitted to reporters late Thursday that a lot of factors have to break the senator's way for victory. But he also was confident they would, given that Scott's initial lead on the night of Election Day shrank from about 60,000 votes (out of nearly 8.2 million cast) to fewer than 13,000.

"It's never been our view that there was going to be one silver bullet that was going to change the margin in the race," Elias said. "If you look at each stage where the margin has shrunk, it has not shrunk because of one big thing, but rather it has shrunk from a number of smaller things. As we move forward I continue to expect that (12,603) margin to go down and disappear entirely."

Here's a look at some of the obstacles facing Nelson:

The hand recount is not going his way

There are about 65,000 questionable ballots statewide to examine in the hand recount, according to the Florida Secretary of State's office. Nelson would have to win about 60 percent of those votes to take the lead.

The recount is examining ballots with "overvotes" (where the machine did not tabulate it because both candidates were chosen) and "undervotes" (where the machine did not tabulate it because no one was chosen).

A human review of an overvote ballot could show if the voter intended to pick one candidate over the other. The belief was that could help Nelson because the county overwhelmingly voted for him against Scott, who is Florida's governor, and those disputed ballots would break the same way.

CLOSE

Florida's battle for the U.S. Senate is headed to a legally required hand recount (Nov. 15)
AP

The recount in Broward was finished after just two hours Friday. Election officials didn't immediately release results, but the speed with which the recount was conducted suggests most of the ballots were undercounts. That doesn't help Nelson because those are votes that won't be counted.

In fact, the news got even worse for Nelson. Of the roughly 65,000 votes being reviewed, 62,257 – or about 95 percent – were undervotes. With fewer than 3,000 votes up for grabs, Nelson will have to find "silver bullets" in other places to scrounge up the difference.

Courts offer little remedy

Nelson will need the courts to side with him in his effort to give counties more ballots to count and more time to tabulate them.

The senator gained one court victory earlier this week when U.S. Chief Judge Mark Walker ordered Secretary of State Ken Detzner to give voters whose ballots were tossed because their signatures didn’t match what was on file until 5 p.m. Saturday to "cure" their ballots. The 11th Circuit Court of Appeals sided with Nelson after a GOP appeal.

But the judge denied a request by Nelson to extend Thursday's 3 p.m. machine recount deadline. Palm Beach County was unable to finish in time. So now Nelson is seeking a hand recount of each of the nearly 585,000 ballots in the county – a process that likely would take weeks.

Walker also denied a request to give election monitors more flexibility in divining voter intent during the hand recount. And he threw out a motion by the Florida League of Women Voters to have Scott recuse himself from the recount process and step down as governor.

Still pending was Walker's motion on a lawsuit from VoteVets demanding that domestic vote-by-mail ballots, which must be received by the day of the election, be treated the same as overseas ballots, which can be received as late as 10 days after the election.

“Citizens in the U.S. should be given the same opportunity as expatriates living abroad,” Elias said.

Time running out

Nelson has less than a week to pull off a win. Or at least buy more time.

Counties have until noon Sunday to finish their hand recounts on the Senate race. Then on Tuesday, the state Elections Canvassing Commission, consisting of the governor (who has recused himself) and two cabinet members, meets to certify the Nov. 6 election official returns.

There’s also a Nov. 30 deadline for any candidate, voter or taxpayer to contest election results in circuit court.

Zelden, the election expert, likened Nelson's chances to a player in a card game betting all his chips on a specific card being pulled from the deck.

"He's literally depending on it to be the queen of hearts," Zelden said. "Anything else, he loses. Sometimes it shows up, but the odds are pretty good it's not going to."